How to delete the Inbound Delivery orderand return the qty back to PO .

For some reason the inbound delivery was completely processed and GR posted, but Handling units do not exist anymore, thus cannot reverse the GR posting for this delivery.Unfortunately we deleted the HU from the delivery .When tried to reverse using VL09 error message pops up that 'There is no material document that can be cancelled in these HUs history' . Seeking your advises how to solve this issue .